Recording and reproducing of sounds



April 5, 1927.

C. F. SACIA RECORDING AND REPRODUGING on souuvs Filed May 5, 1924 fly]FQPQQ cocoon Phoio el. Cell GridPofential 0 Confrol VoltagaL I PaengeaApr. 5, 1927.

UNITED STATES PATENT OFFICE,

CHARLES I. SACIA, OF NEW YORK, N. Y., ASSIGNOR '10 WESTERN ELECTRICCOMPANY INCORPORATED, 01' NEW YORK, N. Y., A CORPORATION 01 NEW YORK.

RECORDING AND REPRODUGING OI SOUNDS.

This invention relates to sound recording and reproducing systems, andparticularly to methods of and means for recording and reproducingsounds having a wide range of intensities.

As is well known, there is a fairly definite limit to the range ofintensity of spoken or musical sounds that can be satisfactorilyrecorded by present known means, such as the phonograph record and thephotographic. film. This .is due inpart at least, to overload distortionat large amplitudes and to the suppression of important high frequencycomponents by the insufiicient resolving power of the recordingmaterial, the phonograph disc, the photographic film, etc. It isdesirableto greatly increase the inten-' sity range of recording, forexample, in the case of talking moving pictures and the good qualityreproduction of orchestra Il'lllSlC.

An object of this invention is to provide a method of and means foraccurately recording sounds having a wide-range of amplitudes usingresent known means.

A further obJect is to provide a. method.

of and means for accurately reproducing the original sounds fromthefrlfecords obtained in such a recording process.';

The invention provides for making two records of the sounds, (a)*.'arecord of the sound reduced to an arbitrary or artificial standardintensity irrespective of the actual intensity of the sounditself, and'(b) a record of the intensity of the sound. Furthermore, it providesthat in "the production of the (alrecord the instantaneous am litudes ofthe recorded sound; Variations s all be controlled by the same energywhich produces the (6) record. In the reproduction, the two records areutilized. the output of the (a) record being controlled by the output ofthe (6) record in such a way that variations in intensity, which wereremoved in the production of the (a) record, are

reinserted and an exact reproduction of the original sounds both in waveform and in intensity is obtained.

These methods. 'appl most readily to elec trical means of recor ing andreproducing sounds and \vill'beillustrated in that way, although theyare not necessarily limited to such means. -A recording circuitcomprising a telephone transmitter, an amphfier, a vacuum tube rectifierand a low pass filter may be used for transforming the sound energy intoelectrical energy and forfurnishing the current for o crating a suitablerecording device for ma ing the (6) record. The variations in therectified current output of this circuit wil be directly pro or- .tionalto the variations in the intensity 0 the sounds received by thetransmitter and the (6) record will, therefore, bean accuraterecord ofthese variations in intensity. In obtaining the (a) record, that is, arecord of the sound reduced to a standard constant intensity, theinvention makes use of the fact that the amplification of a. thermionicamplifier of the audion type depends upon the voltage impressed upon thegrid or in put circuit. A recording circuit comprising a telephonetransmitter, an amplification regulator and an amplifier in connectionwith a suitable recording device is used for making the (a) record. Thetelephone transmitter used in the (a) circuit may be the same one usedin the (b). circuit, or a separate transmitter may be used for eachcircuit as shown in the accompanying drawing. The output of the lowpass,- filter 'in the auxiliary recording circuit used for making the(6) record, described above, is used for furnishing low frequency,rectified voltage to regulate the potential on the grid of regulator,the regulation, however, being .the

reverse of that ,in the recording system. The output of the (a) recordis also impressed on the input circuit of the "amplification regulator.Then, the variations in represente representation of the amplificationregulator used in the recording and reproducing circuits shown in Figs.1 and 4, respectively. Fig. 3 shows the characteristic curves of anelectron discharge device for illustrating the operation of theamplification regulator shown in Fig. 2. 'Fig. 4 is a diagrammaticrepresentation of a sound reproducing arrangement embodying theinvention. Fig.

- 5'shows a section of film indicating one form of sound record obtainedusing the arrangement shown in Fig. 1.

Referrin to Fig. 1, a source of variations, by the telephone transmitter1 is connected to the input circuit of the amplification regulator 3,the output circuit of which is connected to the input circuit of theamplifier 4. The output circuit of the amplifier 4 is connected to themovable wires of alight valve 5 arranged to vary the quantity of lightfrom'a source 6 falling on a film 7, in accordance with the variationsof current received. Similarly, the source of signals, represented bythe transmitter 8 is connected to the input circuit of the amplifier 9,the output circuit of which is connected to the input circuit of avacuum .tube rectifier 10. The output circuit of the rectifier 10 .isconnected to the input circuit of a low pass filter L'PF, the outputcircuit of which is connectedto the movable wires of a light valve 11arranged to vary the quantity of light from a source 12 falling on thefilm 7, in accordance with variations in the current received. Theoutput circuit of the low pass filter LPF is also connected to thecontrol terminals of the amplification regulator 3.

The transmitters 1 and 8 are preferably of the t e described in thearticle entitled The ensitivity and Precision of the ElectrostaticTransmitter for Measuring Sound Intensity, by E. C. Wente, published inthe Physical Review for May, 1922, and their circuits are preferably asdescribed in that article. The amplification regulator 3 is describedlater.

uum tube type. .The rectifier 10 may also be of the three electrodevacuum tube type,

The amplifiers 4 and 9 maybe of the well known-three-electrode vac-' thegrid of which is maintained predominantly negative. The recorders 5 and11 may be any suitabletype but are preferably of the type shown in Fig.1 and illustrated and described in detail in the copending applicationof E. C. \Vente, Serial No. 635,886, filed May 1, 1923, which type isadapted for making sound records on photographic films. The low passfilter LPF may be of the type disclosed in U. S. Patent to G. A.Campbell, No.-1,227,113, dated May 22, 1917, and preferably designed topass frequencies ranging from zero to the neighborhood of 10 cycles, orin some cases up to 50 cycles depending on the nature of the sound to berecorded.

The circuit and apparatus having been generally described, its exactnature will be more clearly understood by a detailed description of itsoperation. Sound variations received by the transmitter 1 are suppliedto the input circuit of an amplification regulator 3, repeated in itsoutput circuit, and amplified by the amplifier 4. The correspondingvariations in current in the output circuit of the amplifier 4 aretransmitted through the conductors of the light waves 5 causingvariations in the width of the slot in the valve 5 corresponding to thevariations in current received, thereby va-. rying the quantity of lightfrom the source 6 transmitted through the slot. This light is focused ona continuously moving film 7 to produce a series of striations ofvarying intensity, corresponding to thesound variations, constitutingthe (a) record of the sounds to be recorded. In a similar manner, soundvariations received by the transmitter 8 are supplied to the inputcircuit of an amplifier 9 and repeated in its output circuit. Thevariations in the outputlcircuit of the amplifier 9 are supplied to theinput circuit of the rectifier 10, and the corresponding rectifiedvariations in its output circuit are transmitted through the low passfilter LPF to the light valve 11, which in the same manner as describedfor light valve 5, causes the (6) record to be recorded on the film. Thevariations recorded on this record will be directly proportional to thevariations in intensity of the sounds received by the transmitter 8. Theoutput of the low pass filter LPF besides furnishing the current foroperating the recorder 11 for making the (6) record is connected to theinput circuit of the amplification regulator 3 in the circuitfor makingthe (a) record to furnish a slowly varying rectified voltage to the gridof the regulator to control its amplification. The amplificationregulator, which 1 is described in detail below, operates in therecording system 'so'as to cause weak ami 'plifications of loud soundsand strong amplificationsof faint sounds. "Thus, the (b) record will bea-re'cordof the variations in intensity of the sounds receiv'ed-b y thetrans-- mitter, while the (a) record will be a record of-the soundsreduced to'aconstint standard intensity. The two records may be on thesame unit (possibly even on the same track); as illustrated in Fig. 1,or they may" be made on different units suitably synchronized. Theformer method which is the preferred method, has been specificallyillustrated.

It may be necessary to cause operation of A the circuit usedfor makingthe (a) record is K times the frequency, the time lag is second.

fThe theory covering t e operation of the regulator can be best shown byconsideration of the characteristic curves 0 a vacuum tube amplifier asshown in Fig. 3. Suppose a vacuum tube is connected to a low impedanceoutput the amplitude of the superimposed alternating current waves beingsmall .enough not to be distorted by this impedance relation, then itscharacteristic curves will be like those shown in Fig. 3. Theupper curvegives the relation between the internal re-- sistan'ce of the tube andthe grid potential,

and the lower curve the relation between the amplification of thetubeand the grid potentia The amplification is where a is the amplificationconstant of the tube, R is the external resistance, and R is theinternal resistance of the tube. As shown by the curves, theamplification is approximately inversel pro ortional to the internalresistance of t e tu e, and over a considerable range can be made to beproportional to the grid voltage. Therefore, a negative voltage appliedto the grid willcause a decrease in the plate current, an increase inthe internal resistance, and hence a decrease in the amplification inproportion to the applied grid potential within the range indicated.

Referring now to the circuit of the ampli: fication re lator shown inFig. 2, 13' is a vacuum tu amplifying device comprising a cathode 14,anode'15 and a control electrode 16. The cathode 14 is heated to'incandescence by battery 17, and is maintained positive with respect tocontrol electrode 16 battery 18.- The input circuit of the will nowamplifier 13'inclu'de's the cathode 14, resistance 19,) esistance 20,battery 21, and the control electrode 16. The output circuit of the amlifier 13 includes the anode 15, the adjusta le resistance 22, thebattery 18, and the cathode 14. The adjustable resistance 22 may be usedfor varying the external resistance in the output circuit.

In operation in the circuit as shown in Fig. 1 sound variations from thetransmitter 1 are impressed on the input circuit across the resistance20 and are repeated in the output circuit of the tube. he output of thelow pass filter LPF, is connected across the resistance 19 to furnishthe varyingrectified control voltage for varying the grid 1 potential.The leads from the low pass filter LPF are so connected, that anincrease in the drop across the resistance 19, caused by an increase inthe current received from the low pass filter LPF, will cause anincrease in the negative voltage applied to the grid, an increase in theinternal resistance of .the tube, and therefore a decrease in theamplification. However, as mentioned above, when the. amplicationregulator is used in the reproducing circuit shown in Fig. 4, the leadsfrom the amplifier 32 are so connected across the resistance 19 that anincrease in the drop across the resistance 19, caused by an increase inthe amplified current received in the reproduction of the (1)) record,will cause a decrease in the negative voltage applied to the grid, 9.decrease in.

the internal resistance of the tube, and, therefore, an increase in theamplification. When the amplification regulator is used in the recordingsystem-of Fig. 1, the direct current component of its output current isprevented from passing to the amplifier 4, by the condenser 23.Likewise, when the regulator is used in the reproducing circuit of Fig.4, the direct current component of its output current is prevented, frompassing to the amplifier 34 by the condenser 23. Thus, in the recordingsystem shown in Fig. 1, loud sounds received .in the transmitter whichcause weak amplification and faint sounds strong amplification, while inthe reproducing system shown in Fig. 4, the regulating action isreversed This regulating device may be made part of the first stage ofthe amplifier, as shown in Fig. 2, or maybe used as a separate unit inconjunction with an amplifier. The regulation can be applied to morethan one step if desired, hence a tamed.

The re roducing system shown in Fig. 4 described. The film 24 is shownpositioned between a light source 25 and the photoelectric cells 26 and27. This film,

very large range of amplification can be obshown in more detail in Fig.5, is a positive made from a negative film produced in the recordingprocess, and contains on its surin theopaque screen 29, andtransparencies in the film 24, are focused by lenses 3'0 and 31 upon thephotoelectric cells 26 and 27, respectively. The photoelectric cell 26is connected to the input circuit of the amplification regulator 32. Thephotoelectric cell 27 is connected to the input circuit of an amplifier33, the output circuit of which is also connected to the input circuitof the amplification regulator 32. The output circuit of theamplification regulator 32 is connected to the input circuit of anotherampli:

fier 34, the output circuit of which is connected to the soundreproducer 35. The amplifiers 33 and 34 and the amplification regulator32 are similar to the corresponding apparatus described in connectionwith Figs. 1 and 2. The sound reproducer 35-1nay be of any suitable typefor example, such as a. telephone receiveror loud speaker.

The circuit and apparatus used in Fig. 4 having been generallydescribed, its enactnature will be more clearly understood by a detaileddescription of its operation. The light rays from the source 25transmitted through the lens28 apertures in the opaque screen 29, andthe transparency of the film 24, and focused on the photoelectric cell26, cause the current from the battery 36 How- :ing through thephotoelectric cell 26 to vary in accordance with the striationscorrespnd- F ing to the (a) record on the film 24,which variations areimpressed upon the input circuit of the amplification regulator 32.

Similarly, the light rays from the source 25 transmitted through thelens 28, other apertures in the opaque screen-129, and the transparencyof the film 24, and focused on the photoelectric cell 27 by the lenses30 and 31 cause the current from the battery 37 flowing throughphotoelectric cell 27 to vary in accordance with the striationscorresponding to the (b) record on the film 24. These variations areimpressed upon the input circuit of amplifier 33, repeated in its outputcircuit, and supplied to the grid of the amplification regulator 32,;varying the amplification in accordance with the variations in the (1))record. The operation of the amplification regulator is the reverse ofthat obtained in the recording, as explained above in connection withthe description of the operation of the amplification regulator shown inFig. 3, the variations in intensity, which were removed in theproduct-ion of the (a) "record in the recording system, beingreinserted. The variations the output circuit of the amplificationregulator 32 are amplified by the amplifier 34 and supplied to the soundreproducer 35, which reproduces the original sounds recorded over a widerange.

or intensity.

tric cell 26 and the amplification regulator 32 to have a slight phaselead over the 0 eration of the circuit including the photoe ectriccell.27 and the amplifier 33 to insure due action of the amplificationregulator. This time lag may be produced by mechanical adjustment, bymeans of. an electrical network, or by any system which possesses a haselag proportional to the frequency. The systems tabove illustrated anddescribed should be construed merely as typical and not as limiting theinvention, the scope of which is defined in the appending claims.Although for convenience of description, the (a) record has beenreferred to in the "specification as reduced to a constant standardintensity or amplitude, this intensity oramplitude need not be constant,but may be arbitrarily 'changed to any desired value.

What is claimed is:

1. The method of recoi ding waves which comprises producing a record ofthe variations in amplitude of the waves and pro ducing another recordof the structure of said waves modified as to amplitude.

2. The method of recording waves which comprises producing a. record ofthe varying amplitudes of. the waves and producing another record of theharmonic structure of said waves reduced to an arbitrary standardamplitude.

3. The method of recording waves which comprises producing a record ofthe am litudes of the waves and producing anot ier record of theinstantaneous phase variations of said waves, said other record beingreduced to an arbitrary amplitude.

4. The method of recording sound, which comprises producing a record ofthe variations in intensity of the sound and producing a second recordof the sounds reduced to an arbitrary standard intensity.

5. The method of recording sound waves which consists in producingarecord of the amplitudes of the sound waves,'-. and produc- 7. Themethod of recording waves which consists in amplifying the waves,regulating the degree of amplification of said waves in accordance withvariations in am litude of said waves, utilizin said ampli ed waves formaking a recor of the harmonic structure of said waves, and producinganother record of the variations in amplitude of said waves.

source of waves of vary 8. The method of recordin waves, which comprisesproducing a uni- 'rectional pul-' sating current varying in accordancewith variations in the amplitude of the waves,

utilizing said current to make a record of said variations in amplitude,amplifying said waves, utilizing said current also to nontrol the degreeof am lification inversely as the amplitude of sai waves and utilizingthe amplified waves for ma 'ng a second record of the waves.

9. In a recording system, a source of waves, means for recording thevariations in am litude of said waves, and means..for

' the structure of said waves, means for controlling the amplitude ofsaid waves in accordance with the intensity of sounds, and means. forrecording variations in said sound intensities.

12. A recording system comprising a amplitudes, an amplifier suppliedwith said waves, means for regulating the degree of amplificationimparted to said waves, a wave responsive device arrangedto control saidregulating means in accordance with variations in intensity of saidwaves and a recording device controlled by said amplifier.

13. A recording system which comprises a source of waves of varyingamplitudes, an am lifier supplied with said waves, means or regulatingthe degree of amplification of said waves, a wave responsive devicearranged to control said regulating means in accordance with variationsin amplitude of said waves, a recording device controlled b saidamplifier, and means for recording t e variations in amplitude of saidwaves.

14. In combination, a source of waves, an amplifier supplied with saidwaves, means for supplying a uni-directional, pulsating voltage varyingin accordance with the amplitude of said waves to said amplifier forregulatingthe degree of amplification of said waves, and a recordingdevice. controlled by said amplifier. l

15. In a recording system, a sourceof waves, an amplifier supplied withsaid waves, means for *producing a uni-directional, pulsating current oflow frequency varying in accordance'with variations in amplitudeofsaidwaves, a recording device controlled by said current,- the degree ofamplification of said waves supplied to said amplifier being alsocontrolled b said cur rent, and a second recording evice controlled bysaid amplifier.

16. In a recording system, a source of. sound waves, means for obtainingan amplified, rectified current varying in accordance with variations inthe amplitude of said waves, a recording device controlled by saidvarying current, an amplifying device supplied with said waves. aregulating device supplied with said rectified current for con-'trolling the amplification of said waves suppl 1ed to said amplifyingdevice in accordance w1th variations in said current, and a secondEecording device controlled by said ampli- 17. In a recording system, asource of i sound waves of varying intensity, a regulatmg devicesupplied with said waves, means for varying the amplification of saidwaves supplied to said regulating device inversely as the intensity ofsaid waves, means for recording the waves as modified by said firstmentioned means, and means for making a a record of variations inamplitude of said sound waves 1 18. A method of producing a wave fromwave records which comprises regulating the output of a record ofcertain characteristics of a wave with the outputof a record of othercharacteristics of said wave, and controlling a receivingdevice with theresultant ontput of said records so that said wave is reproduced withall of said characteristics.-

19. A method of reproducing sound from two sound records upon which arerecorded different characteristics of the same source of sound waves,one of said records representing the harmonic structure of a sound waveand the other of said records representing the varying amplitudes ofsaid wave which comprises transforming the output or each of saidrecords into corresponding-electrical variations, impressing thevariations corresponding to the output of the first mentioned record onthe input circuit of an amplifying device superimposing thereon thevariations corresponding to the output of the second mentioned record ofthe amplitudes of said wave, regulating theamplification of saidvariations corresponding to said first mentioned record with thevariations correa 0 I spondlng to said second mentioned record anotherrecord representing other characteristics of the same wave, a receivingdevice,-

and means for controlling said receiving device with the output of saidrecords whereby a wave is produced having all of the characteristics ofsaid wave.

21. In a reproducing system a record representing the varying amplitudeof a wave,-

.w'a've, a receiving device, and means for controlling said receivingdevice with. said records whereby said wave is reproduced accurately inwave form and amplitude.

23, In a reproducing system, a record of the varying am litudes of asound wave, another record 0 the structure of said wave means forcontrolling the output of said second mentioned record with the outputof said first mentioned record so as to obtain a resultant output havingthe same amplitudes and thesame wave form as said sound wave, and meansfor transforming said output into sound energy. I

24. In a reproducing system, a record of the varying amplitudes of asound wave another record of the harmonic structure of said wave, meansfortransforming the output 6: each 61 as wares 'into electrical vdri- Vations, means for amplifying the variations correspondin to the outputof the first men-' resultant outputfandmeans' for trans or ing saidoutput into sound energ.

25. In a reproducingsystem, a record of .the varying amplitudes of asound wave,

another record of the harmonic structure of said wave, means fortransforming the outputof each of said records into electricalvariatio'n's', means for regulating the amplification 'of the variationscorresponding to the second mentioned record with the varia tionscorresponding to the'first-mentioned record, and means for transformingthe re-' sultant variations into sound energy.

In witness whereof, I hereuntosubscribe.

my name this 29th day of April A. D..' 1924.

CHARLES F. SACIA.

